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leftThreshold - SA/4e stereo amplifier

You are reading the review of one of our 5 prefered amplifiers in the world, the THRESHOLD SA/4e.
My co-administrator Nounours18200, says that it is one of the very best transistors amplifier ever built on the planet... Whatever the forum you read a feedback on it, it always gets an excellent ranking, and more precisely, it is always ranked as the cream of the amplifiers.

The THRESHOLD SA-4e was built from 1990 to 1994. It has been a great commercial success in the States but not in Europe simply because the importer put the price at the celling, nearly 75,000 French Francs at this time ... If you give a look at this article 
where we have  estimated what the current Threshold prices would be if they were still manufactured, you would see that 75,000 FF represent more than 16,000€ in 2008: more or less 24,000$­­­­­­­­­­ ! It is therefore easy to understand 2 things:
  • the prices of this kind of amplifiers are totally unreasonable in Europe
  • the manufacturers should seriously look at the final European street price, perform a deep analysis of their authorized importer's margins, and put some order in this market: they would increase their volume of sales incredibly !
The manufacturers should also investigate to understand why the current $­­­­­­­­­­/€ exchange rate is purely and superbly ignored by the Europeans importers... There is a safe way for the manufacturers to largely increase their sales, simply by adjusting the importers margins, oblige their importer to take the current €/$­­­­­ exchange rate in their calculation of the retail price, in order to keep the street price at a more reasonable level (in comparison with the States)....


THRESHOLD SA-4e front view.

Consequently in 2008, this amplifier is very rare on the French market, mine is comming from the USA.

It is a 100W pure class A designed by Nelson PASS, who left this company to create his own PASS LABORATORIES as you surely already know if you use to visit our site.

The THRESHOLD SA/4e is built like a tank: thanks Mr PASS. And when we say like a tank, it means than it is impossible to destroy ! Like all the SA serie amplifiers, the cabinet is unblievable thick and robust: have a look at the SA/6e monoblocks in this article: the mechanical build quality is the same. Outstanding.

Do not try to find the same mechanical buid quality nowdays: since the electronics are designed to match the Finance Directors objectives, and since the internal parts are chosen to match the Purchasing Director cost reduction objectives, there is no way to find this quality anymore.

Maybe the PASS LABS cabinets are still as robust as the SA/4e one, but we know no brand actually manufacturing so impressive cabinets (maybe MBL on their monoblocks amps ?, and PASS on their X.5 serie).


The THRESHOLD SA-4e back view.

Regarding the maintenance, there is no problem at all, as for any Threshold SA amp, there is only few things to do, which are fully normal after 15 years of service:

  • the main power supply capacitors have to be changed (normal after 15 years)
  • the BIAS should be tuned to be pulled back into the manufacturer specifications range, it means between 1.6V to 2Volt.

These points have a huge impact on the final musical result.


sa4e_internal_view.jpgThreshold SA/4e, inside view

There are only a few amplifiers able to correctly drive the Apogee DIVA and all of them are "monsters", with huge possibilities regarding the current delivery: the SA/4e can deliver more than 35 amps continuously !.

The SA/4e has 26 transistors for each side (i.e 26 transistors per channel), the well known bipolar MOTOROLA MJ15011 et MJ15012 , each of them being able to deliver 10 A (250V) and 200W ... Consequently, the stability of the SA/4e is outstanding, regardless the impedance caracteristics of the loudspeakers.


System used for review is the Reference system #2:

CD player : WADIA 850, Preamp JADIS JP80MC, Loudspeakers APOGEE DIVA (the ribbons have been changed for new ones), interconnect cable silver SILTECH 4-80S , speaker cable silver SILTECH LS2-090.


How to be in the right way with the sound of SA/4e :

First of all, all the tips given in this article remain true, but there a few other things to know to get the best from the SA/4e.
The Preamplifier is absolutely critical: the SA/4e does not work correctly if you have a "poor" preamplifier.
Do not use a passive preamplifier nor the CD player direct output, the musical result would be a disaster. All the Threshold SA serie amps require a true and high end preamp, particularly because their input impedance is a bit low.

As usual with a new amplifier, I have changed / upgraded some internal components.

First of all, the power supply main capacitors which were too old and had to be replaced (it is fully normal after 15 years of service). The original ones were 27,000µF x 6, but I did not  find the same value (more precisely, there is not enough space inside the SA/4e cabinet for housing 6 x 27,000µF new high quality capacitors) so I took 6 x 22,000µF.

Regarding the driver stage, I have changed also some transistors and zener diodes for new ones, with better caracteristics.

I have not forgotten to put 4 small capacitors from Vishay (0.47µF) in // on the main 22,000µFpower supply ones, as it has already been explained in the SA/3.9e and T2 upgrades articles.
You also need to seriously burn in the SA/4e internal components, and also to tune your other devices before getting the best result.


As an example, find herebelow 2 pictures of a SA/4e recently upgraded by FIDETECH:

The SA/4e when it arrived at the facility:



and the same one after it has been upgraded by FIDETECH:



With the SA/3.9e, I had changed the tubes of my preamp to the Telefunken 12AX7. With the SA/4e, the best reult is achieved with the GT Groove 12AX7 tubes which perfectly match with the SA/4e.

During the transition period from the upgraded SA/3.9e to the SA/4e, I have also discovered  a simple trick that I have described in the Apogee side (left bar). It was to validate HP cable (red and black) in a new dispatch. And the sound is better !

Amongst all the Solid State amplifiers I have eard to date, and I have lessoned to a lot of them (...), I have to say that the SA/4e is IMHO, the best one.

Why ? simply because  it is very difficult to find any area in which it is not excellent.

Eveything is very linear, you do not have any excess of medium or bass. With this straight line, you will discover a lot of informations in many CD's that are not present with other poor amplifiers.

You will also discover that a lot of CD are not well recorded. You will be very surprised that there is some portion of your favorite CD that have a 3D aspect totaly new now.

It seems that it has also no grain, and of course the sound is beautiful compared with the KRELL KSA 50 MKII.

For the cons, I would say that the bass are so well maintained in a velvet glove that it seems they are not enough present  under 40Hz.
Do not forget that I have panels with only 87dB of efficiency, and panels are not known for delivering huge bass. See Quad and other manufacturers !...

I am still searching for a bad area but ... there is not !

If I compare it with the upgraded SA/3.9e, I must said that SA/4e has a more extended bandwidth, whereas the SA/3.9e is more medium focused.

The power measured on my SA/4e is not 100W in class A, but 120W. And the energy is uniformly delivered everywhere on the bandwdith, so it seems that the power is inferior of the SA/3.9e. In fact, with more power, you have more ability to drive panels effortless.

I am astonished every day by this SA/4e....




  • it is a prince in the Solid State transistors amps arena
  • medium very sweet, really magic.
  • huge bandwith
  • very stable: like a rock
  • exceptional everywhere on the bandwith
  • I have never found before the same qualities on a SS amplifier: this kind of fullness is incredible (on vacuum tube, yes you can more easily find it !)
  • the final price after its upgrade is still an incredible bargain compared to the amps that are still manufactured actually...: you simply CANNOT find a new amplifier able to compete with an upgraded SA/4e at the same price. This is a fact, no doubt.


  • bass are beautiful but not in the same league as KRELL
  • I try to find everyday but I find nothing...

My search never ends, but the THRESHOLD SA/4e  is a really an exceptional amplifier and you will have also no maintenance and no tubes to changed every 5000 hours.


Article writen by  Florent .

Creation date : 19/05/2008 @ 17:43
Last update : 09/11/2014 @ 20:28
Category : Threshold
Page read 2369 times

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Reactions to this article

Reaction #6 

by Nounours18200 10/09/2011 @ 18:18

I (strongly) believe that the solution 2 is better : the SA/3.9e are very nice class A amplifiers that will excel in the mid and high frequencies, and will undoubtly beats the S/550. This last one is more appropriate for driving the bass.
Hope this helps,

Reaction #5 

by BasBass 10/09/2011 @ 16:40

Thanks for your infos...
I have the idea to use two amplifiers to bi-amp my B&W 802D in two different ways:
1 - To use two identical S/550e, one for each loudspeaker, in "vertical" bi-amping.
2 - To use one S/550e only for woofers in the bass range and one S/A 3.9e only for midranges and tweeters in mid/high range in "Horizontal" bi-amping.
What is the best solution based on your experiences?
Thanks in advance


Reaction #4 

by Nounours18200 10/09/2011 @ 14:54

Hello Giovanni,

Yes of course, it is possible to make the same kind of upgrade for your S/550e.
There is no "standard instructions" for such an upgrade, it is a matter of expertise.
If you do not have the necessary knowledge to perform it by yourself, the simplest way is to ask a (really) goo d technician knowing how to proceed.
If you do not know a skilled technician (take care, it has to be familiar with the big solid state amps), just send me an email or MP, and I will give you the necessary information and contact name.


Reaction #3 

by BasBass 10/09/2011 @ 00:52


I would like to know if it's possible to make the upgrade you have show (on the SA/3.9e too) on my S/550e. I hope...nn
If yes where can I find the complete instruction to do this?
Many many thanks


Reaction #2 

by Nounours18200 20/02/2009 @ 22:18

Probably because you have sold your SA/4e to somebody, maybe directly to Florent ... There is no other explanation.... e
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